Planar illumination device and liquid crystal display device using the same

ABSTRACT

A planar illumination device for illuminating a liquid crystal display panel provided with a polarizing plate on a light incident side, includes: a light source unit for emitting light having a specified polarization direction; and a light irradiating member for deflecting light emitted from the light source unit and irradiating the liquid crystal display panel with the deflected light, wherein the light irradiating member deflects the light emitted from the light source unit such that the polarization direction of the light emitted from the light source unit substantially coincides with a transmission axis direction of the polarizing plate of the liquid crystal display panel.

This is a Rule 1.53(b) Divisional of application Ser. No. 12/439,435,which is the National Stage of International Application No.PCT/JP2007/068053, filed Sep. 18, 2007.

FIELD OF TECHNOLOGY

The present invention relates to a planar illumination device suitableas a backlight of a thin flat display used in a television set or thelike, and a liquid crystal display device using the same.

DESCRIPTION OF THE BACKGROUND ART

Conventionally, backlight illumination devices utilizing a cold cathodefluorescent tube have been widely used in liquid crystal display devicesusing liquid crystal display panels. In recent years, attention has beenfocused on backlight illumination devices using three color lightemitting diodes (LED devices) of red, green and blue lights for thereproduction of more clear and natural color tones, and the developmentthereof has been vigorously promoted.

A planar illumination device of the lateral light source type so-callededge light type in which light from a light source is incident through aside surface (light incident surface) of a light guide plate and lightis emitted from one principal surface (light output surface) of thelight guide plate for illumination is used as a backlight illuminationdevice with a relatively small size. On the other hand, a directillumination device in which cathode fluorescent tubes or LED devicesare arranged in a planar manner is used for backlight illuminationrequiring a large size and a high luminance.

A demand for liquid crystal display devices with thin and large screenssuch as wall mounted TVs is thought to increase in the future. However,in order to realize this, direct illumination devices have a problem ofbeing difficult to be thinned and edge light type illumination devicesusing conventional light sources have a problem of being unable toensure a sufficient luminance if screens are large.

To realize a liquid crystal display device with a thin large screen,researches have started on an edge light type backlight using a laserlight source, which provides high luminance and which is suited for ahigh power output.

Furthermore, in order to realize a still higher luminance and lowerpower consumption, the methods for better utilization of a backlightillumination has been considered. For example, Patent Document 1discloses a method improving the light utilization efficiency of aliquid crystal display device by providing LEDs with polarizationanisotropy.

However, the foregoing conventional structure of Patent Document 1 hasthe following drawbacks. That is, according to Patent Document 1, sincea light is incident on a light guide plate from only one direction, aproblem of non-uniform luminance is liable to occur when applied to alarge size screen. A problem of non-uniform color is also liable tooccur due to differences in absorption when three color lights, i.e.,red, green and blue lights propagate in the light guide plate.

As described above, the enlargement of thin flat displays represented byplasma displays and liquid crystal displays have been promoted at arapid pace in recent years. A direct illumination device in whichcathode fluorescent tubes are arranged in a planar manner has beenconventionally used as a backlight of a liquid crystal display devicerequiring a large size and a high luminance. Power consumption thereoftends to increase substantially in proportion to the screen size.Furthermore, the power consumption of the backlight accounts for thelarge proportion of the total power consumption of the liquid crystaldisplay device, and the problem of the power consumption has been acurtail issue for the liquid crystal display device.

In recent years, attention has been also focused on backlightillumination using light emitting diodes (LED devices) of three primarycolors for the reproduction of more clear and natural color tones.Incidentally, a planar illumination device of the lateral light sourcetype, a so-called “edge light type” has been used as a conventionalbacklight illumination device with a relatively small size wherein alight emitted from a light source is incident on the light guide platethrough a side surface thereof and a light is outputted from oneprincipal surface of the light guide plate to be used for illumination.Here, an attempt has been made to apply the foregoing edge light typeillumination device to a thin large screen by adopting high-output laserlight sources. However, such applications adopting the light-outputlaser light sources have a drawback in that the required powerconsumption is larger than that of cathode fluorescent tubes at present,and a reduction in power consumption is therefore a critical issue.

In response, various methods have been proposed to realize a reductionin power consumption. examples of which includes the method of reducingthe power consumption by controlling the backlight luminance by limitingthe maximum luminance of the backlight, or the method of reducing thepower consumption by improving the utilization of the backlightluminance utilizing polarized lights (for example, Patent Document 1).

However, there still exists a strong demand for a reduction in powerconsumption, and with the foregoing conventional methods, the powerconsumption cannot be reduced to a sufficient level to meet suchdemands.

Patent Document 1:

-   Japanese Unexamined Patent Publication No. 2006-40639

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a planar illuminationdevice, which realizes a high light utilization efficiency and low powerconsumption by improving the transmission efficiency of a liquid crystaldisplay panel.

A planar illumination device according to one aspect of the presentinvention for illuminating a liquid crystal display panel provided witha polarizing plate on a light incident side, includes: a light sourceunit for emitting light having a specified polarization direction; and alight irradiating member for deflecting light emitted from the lightsource unit and irradiating the liquid crystal display panel with thedeflected light, wherein the light irradiating member deflects the lightemitted from the light source unit such that the polarization directionof the light emitted from the light source unit substantially coincideswith a transmission axis direction of the polarizing plate of the liquidcrystal display panel.

According to the foregoing structure of the planar illumination device,the liquid crystal display panel is irradiated with the light emittedfrom the light source unit in such a manner that the polarizationdirection thereof is brought into substantially coincide with thetransmission axis direction of the liquid crystal display panel. Withthis structure, the transmission efficiency of the liquid crystaldisplay panel can be improved, thereby realizing a light utilizationefficiency while reducing power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a schematic structure of a planarillumination device according to the first embodiment of the invention;

FIG. 2 is a section showing a schematic structure of a liquid crystaldisplay panel;

FIG. 3 is a diagram showing polarized lights of incident lights andoutput lights on and from a light guide plate;

FIGS. 4A and 4B are a rear view and a side view showing a schematicstructure of a planar illumination device according to the secondembodiment of the invention;

FIG. 5 is a rear view showing a schematic structure of a planarillumination device according to the third embodiment of the invention;

FIG. 6 is a diagram showing polarized lights of incident lights andoutput lights on and from a light guide plate used in a planarillumination device according to the fourth embodiment of the invention;

FIG. 7 is a section showing a schematic structure of a light guide plateused in a planar illumination device according to the fifth embodimentof the invention;

FIG. 8A is a perspective view showing a schematic structure of a lightguide plate used in a planar illumination device according to the sixthembodiment of the invention, FIG. 8B is an enlarged plan view of a partB of FIG. 8A and FIG. 8C is an enlarged section of a part A of FIG. 8A;

FIG. 9 is a perspective view showing a schematic structure of areflecting plate used in a planar illumination device according to theseventh embodiment of the invention;

FIG. 10A is a perspective view showing a schematic structure of adisplay unit of a liquid crystal display device according to an eighthembodiment of the invention and FIG. 10B is an enlarged perspective viewof a part C of FIG. 10A;

FIG. 11A is a front view showing the outer appearance of a liquidcrystal display device provided with the display unit of FIG. 10A, FIG.11B is a diagram showing a connection relationship of a human detectionsensor, light source units of a backlight and a controller and FIG. 11Cis a block diagram showing a schematic structure of the controller ofFIG. 11B;

FIGS. 12A and 12B are enlarged perspective views of a light source unitof a backlight used in a liquid crystal display device according to aninth embodiment of the invention;

FIG. 13 is an enlarged side view of light source units of a backlightused in a liquid crystal display device according to the tenthembodiment of the invention;

FIG. 14 is a perspective view showing a schematic structure of a displayunit of a liquid crystal display device according to the eleventhembodiment of the invention;

FIG. 15A is a perspective view showing a schematic structure of a lightguide plate of a backlight used in a liquid crystal display deviceaccording to the twelfth embodiment of the invention and FIG. 15B is anenlarged plan view of a part D of FIG. 15A; and

FIG. 16A is a side view showing a schematic structure of a backlightused in a liquid crystal display device according to a thirteenthembodiment of the invention and FIG. 16B is a rear view of the backlightincluding a part E of FIG. 16A.

BEST MODES FOR EMBODYING THE INVENTION

Hereinafter, embodiments of the present invention are described withreference to the drawings. It should be noted here that the membershaving the same structures and the functions are designated by the samereference numerals, and explanations thereof may be omitted forconvenience for explanations.

First Embodiment

FIG. 1 is a perspective view showing a schematic structure of a planarillumination device according to the first embodiment of the presentinvention. FIG. 1 shows a liquid crystal display panel 6 to beilluminated with the planar illumination device of the presentembodiment and prism sheets 4, 5 arranged between the planarillumination device of the present embodiment and the liquid crystaldisplay panel 6 in addition to the planar illumination device of thepresent embodiment.

As shown in FIG. 1, the planar illumination device according to thepresent embodiment includes linear light source units 1 a and 1 b,cylindrical lenses 2 a and 2 b, and a light guide plate 3. The linearlight source unit 1 a includes two laser light sources arranged in theY-direction in FIG. 1, and laser lights emitted from the respectivelaser light sources are outputted to the cylindrical lens 2 a whilebeing converted into linear lights, for example, using cylindricallenses (not shown). The respective laser light sources of the linearlight source unit 1 a emit lights of three primary colors, i.e., red,green and blue lights. The linear light source unit 1 b includes threelaser light sources arranged in the X-direction shown in FIG. 1, andlaser lights from the respective laser light sources are emitted to thecylindrical lens 2 b while being converted into linear lights, forexample, using unillustrated cylindrical lenses. The respective laserlight sources of the linear light source unit 1 a emit lights of threeprimary colors, i.e., red, green and blue lights.

The cylindrical lenses 2 a and 2 b are made up of Fresnel lenses, whichform lights radially emitted from the linear light source units 1 a and1 b and incident thereon into substantially parallel lights, and outputthem to be incident on the light incident surface of the light guideplate 3. The light guide plate 3 receives lights emitted from thecylindrical lenses 2 a and 2 b through the end surface (the lightincident surface) thereof, and outputs them to the liquid crystaldisplay panel 6 from one of the principal surface thereof. In the lightguide plate 3A, a multitude of isotropic scattering elements having nodirectivity are formed uniformly, whereby the incident lights can beequally polarized in every direction by an optical phenomenon such asreflection, scattering, refraction or diffraction caused by thesescattering elements. The scattering elements can be realized, forexample, by forming scattering particles made of thermosetting resin orthermoplastic resin in the light guide plate 3 or generating bubbles orthe like in the light guide plate 3.

In the present embodiment, the linear light source unit 1 a is arrangedso as to emit respective red, green and blue lights as polarized lightsin the Z-direction, whereas the linear light source unit 1 b is arrangedso as to emit respective red, green and blue lights as polarized lightsin the X-direction. In this example, the laser light sources are usedfor the linear light source units 1 a and 1 b. However, the presentembodiment is not intended to be limited to this structure, and forexample, LED devices which emit lights of three primary colors, i.e.,red, green and blue lights may be used as the light sources. In thiscase, lights emitted from the LED devices may be polarized in thesimilar manner as the laser lights, for example, using polarizingelements.

FIG. 2 shows a schematic structure of the liquid crystal display panel6. The liquid crystal display panel 6 has such a general structure thattransparent electrodes (not shown) and liquid crystal molecules 63 areformed between glass substrates 61 and 62. Further, the polarizing plate64 and the polarizing plate 65 having different transmission axes areformed on the light output side and the right incident siderespectively, so as to sandwich the glass substrates 61 and 62. Thetransmission axes of the polarizing plates 64 and 65 are substantiallyorthogonal to each other. The transmission axis of the polarizing plate65 at the light incident side extends in the X-direction.

According to the planar illumination device of the present embodiment,Z-direction polarized lights as emitted from the linear light sourceunit 1 a are formed into substantially parallel lights in an XY plane bythe cylindrical lens 2 a, and are guided to the light guide plate 3. Onthe other hand, X-direction polarized lights emitted from the linearlight source unit 1 b are converted into substantially parallel lightsin an XY plane by the cylindrical lens 2 b, and are guided to the lightguide plate 3.

The lights entered into the light guide plate 3 are polarized by thescattering elements formed in the light guide plate 3, and are outputtedfrom the light guide plate 3. Here, since the scattering elements areformed uniformly in the light guide plate 3, it is possible to outputuniform lights from the light guide plate 3 by inputting theretosubstantially parallel lights. According to the foregoing structure ofthe present embodiment, since the lights are entered into the lightguide plate 3 from two directions orthogonal to each other, it ispossible to output more uniform lights.

The lights outputted from the light guide plate 3 are incident on theliquid crystal display panel 6 after passing through the prism sheets 4and 5. The prism sheet 4 polarizes an output angle in the X-direction,whereas the prism sheet 5 polarizes an output angle in the Y-direction.Accordingly, the lights emitted from the light guide plate 3 areincident on the liquid crystal display panel 6 after having an outputangle distribution in the X-direction corrected by the prism sheet 4 andhaving an output angle distribution in the Y-direction corrected by theprism sheet 5.

With the conventional planar illumination device using cathode tubes orLEDs, since the lights incident on the liquid crystal display panel arenot polarized, an amount of lights passing through a polarizing plate onthe light incident side of a liquid crystal display panel becomes ½ ofthe total amount of incident lights. In contrast, according to theplanar illumination device of the present embodiment, most of the lightsoutputted from the light guide plate 3 pass through the polarizing plate65 on the incident side of the liquid crystal display panel 6, for thereasons explained below.

FIG. 3 is a typical depiction showing polarized lights of incidentlights on and output lights from the light guide plate 3. In FIG. 3, alight emitted from the linear light source unit 1 a is incident on thelight guide plate 3 through a light incident surface 3 a thereof andlight emitted from the linear light source unit 1 b is incident on thelight guide plate 3 through the light incident surface 3 b of the lightguide plate 3, and both of the incident lights are outputted from thelight output source 3 c of the light guide plate 3. The two lightincident surfaces 3 a and 3 b of the light guide plate 3 are provided soas to be orthogonal to each other.

As shown in FIG. 3, the lights respectively entered in the light guideplate 3 through the light incident surfaces 3 a and 3 b are polarized asbeing reflected or refracted by scattering elements 7, and are outputtedfrom the light output surface 3 c.

Here, since the scattering elements 7 are formed in a shape withouthaving any directivity, the lights entered from the X-direction and theY-direction propagate toward the light output surface 3 c with equalefficiency and most of lights are outputted while maintaining thepolarization directions. It was confirmed also with the actualmeasurement that at least 80% of output light maintain their originalpolarization components when polarized light parallel to or vertical toa light output surface is incident on the end surface of the foregoinglight guide plate containing scattering elements.

Accordingly, in the present embodiment, most of the Z-directionpolarized lights entered through the light incident surface 3 a becomeoutput lights having polarization planes in an XZ plane, most of theX-direction polarized lights entered through the light incident surface3 b become output lights polarized in the X-direction.

Since the X-direction polarized lights are not influenced in the prismsheets 4 and 5, the majority of the lights emitted from the light guideplate 3 pass through the polarizing plate 65 at the incident side of theliquid crystal display panel 6 which has the transmission axis in theX-direction. Assumed based on the actual measurement that at least 80%of the lights pass, the transmission efficiency can be improved 1.6times as high as before.

As described above, according to the planar illumination device of thepresent embodiment, uniform luminance can be obtained over a large areaand higher image quality is promoted by making lights incident on thelight guide plate 3 from the two directions orthogonal to each other,and the polarizations of lights outputted from the light guide plate 3can be aligned and the transmission efficiency of the liquid crystaldisplay panel 6 can be improved by specifying incident polarized lightscorresponding to the light incident surfaces of the light guide plate 3.As a result, a liquid crystal display device of lower power consumptioncan be realized.

Second Embodiment

Next, the second embodiment of the present invention is described. Inthe foregoing first embodiment, the linear light source units 1 a and 1b are provided in the outside of the light guide plate 3 as shown inFIG. 1. In the present invention, a light source unit is arranged on theunderside of the light guide plate 3 and lights are incident on thelight guide plate 3 while being polarized by mirrors or the like. FIGS.4A and 4B are a rear view and a side view respectively showing aschematic structure of a planar illumination device according to thepresent embodiment.

As shown in FIGS. 4A and 4B, the planar illumination device according tothe present embodiment includes a light source unit 11, a half waveplate 12, a polarizing beam splitter 13, linearization optical elements14 a and 14 b, prisms 15 a and 15 b and the light guide plate 3. Thelight source unit 11 combines and outputs lights having alignedpolarizations from laser light sources 11 a for three primary colors,and the half wave plate 12 rotates the polarizations of these lightsemitted from the light source unit 11. The linearization opticalelements 14 a and 14 b are made up or lenticular lenses, cylindricallenses or the like, and the prisms 15 a and 15 b are provided forguiding the lights from the linearization optical elements 14 a and 14 bto the light guide plate 3. To these linearization optical elements 14 aand 14 b, cylindrical lenses which convert lights into parallel luminousfluxes are connected.

According to the planar illumination device of the present embodiment,lights emitted from the light source unit 11 are converted intopolarized light having a polarization plane substantially at 45° withrespect to the light output surface 3 c of the light guide plate 3 bythe half wave plate 12, and are output from the polarization beamsplitter 13 after being split into P-polarized transmission light andS-polarized reflected light substantially at a ratio of 1:1 by thepolarization beam splitter 13. The light having passed through orreflected from the polarization beam splitter 13 is expanded in a planesubstantially parallel to the light guide plate 3 by the linearizationoptical element 14 a or 14 b and converted into parallel luminous fluxby the prism 15 a or 15 b to be incident on the light guide plate 3.

According to the planar illumination device of the present embodiment,it is possible to generate linearly polarized light in any arbitrarydirection and to freely change the transmission to reflection ratio bythe polarization beam splitter 13 by adjusting the optical axis of thehalf wave plate 12.

Third Embodiment

Next, the third embodiment of the present invention is described. Thepresent embodiment differs from the foregoing second embodiment in thata light emitted from the light source unit 11 is guided to the undersideof the light guide plate 3 using an optical fiber 3. FIG. 5 is a rearview showing a schematic structure of a planar illumination deviceaccording to the present embodiment.

As shown in FIG. 5, the planar illumination device according to thepresent embodiment includes a light source unit 11, collimator lenses 16and 18, an optical fiber 17, a polarization beam splitter 13,linearization optical elements 14 a and 14 b, prisms 15 a and 15 b and alight guide plate.

In the planar illumination device according to the present embodiment,light from the light source unit 11 is condensed by the collimator lens16 to be incident on the optical fiber 17 and light emitted from theoptical fiber 17 is formed into substantially parallel light by thecollimator lens 18 to be incident on the polarization beam splitter 13.Since the light directed through the optical fiber 17 loses itspolarized nature while being guided by the optical fiber 17, it ispolarized and split into transmission light and reflected lightsubstantially at 1:1 by the polarization beam splitter 13.

Fourth Embodiment

Next, the fourth embodiment of the present invention is described. Inthe foregoing first to third embodiments, lights emitted from the lightsource unit are entered through two light incident surfaces of the lightguide plate, which are provided to be orthogonal to one another. Incontrast, lights emitted from a light source unit are incident throughthree light incident surfaces of the light guide plate in the presentembodiment. FIG. 6 is a typical depiction showing polarized lights ofincident lights on and output lights from a light guide plate used in aplanar illumination device according to the present embodiment. Thebasic structures of the present invention are the same as those of thefirst through third embodiments, and explanations thereof shall beomitted here.

In FIG. 6, lights entered through the light incident surface 3 a and asurface facing the light incident surface 3 a are Z-direction polarizedlights, and lights entered through the light incident surface 3 b arepolarized in the X-direction. Accordingly, in the present embodiment,the lights entered through the light incident surface 3 a and thesurface facing the light incident surface 3 a are outputted as lightshaving polarization planes in an XZ plane, whereas the X-directionpolarized light entered through the light incident surface 3 b areoutputted as X-direction polarized light. As a result, the output lightsof more uniform luminance can be realized.

In the present embodiment, it is possible to realize still more uniformluminance of the output lights by arranging such that lights are enteredalso through the surface facing the light incident surface 3 b. In thiscase, it may be arranged so as to enter the X-direction polarized lightsthrough the surface facing the light incident surface 3 b and to outputthe X-direction polarized lights.

The effect of improving the light utilization efficiency can be achievedalso from the foregoing structure of illuminating in three or fourdirections as in the case of illuminating in two directions. In thiscase, it may be arranged such that the lights entered through thesurface facing the light incident surface 3 a have a polarization planein the XZ-plane and lights entered through the surface facing the lightincident surface 3 b become X-direction polarized light, so that outputlights thereof can pass through the polarizing plate 65 on the incidentside of the liquid crystal display panel. As described, with thearrangement wherein the lights are entered through a plurality of endsurfaces (light incident surfaces) of the light guide plate, it ispossible to realize a still more uniform luminance.

Incidentally, the present embodiment may be arranged such that red, blueand green lights are respectively entered through different lightincident surfaces. For example, in the case of using SHG as a greenlight source, only the green light source has a large size. It istherefore possible to increase the degree of freedom in arrangement byproviding a separate light incident surface for the green light.Furthermore, in the case of adopting a screen with difference in lengthbetween vertical and horizontal dimensions, such as 16:9, for example,the problem of non-uniformity in color due to differences in absorptionin the light guide plate is incident only from the vertical direction.

Fifth Embodiment

Next, the fifth embodiment of the present invention is described. In thepresent embodiment, a polarization hologram layer is arranged at areflecting surface side of the light guide plate according to any one ofthe foregoing first to fourth embodiments. Other than the foregoing, thestructure of the present invention is the same as those of the first tofourth embodiments, and explanations thereof shall be omitted here. FIG.7 is a cross-sectional view showing the schematic structure of the lightguide plate used in the planar illumination device according to thepresent embodiment.

In the present embodiment, the lights entered into the light guide plate3 are gradually emitted from the light output surface by being polarizedby scattering elements 7 while being repetitively reflected between oneprincipal surface (light output surface) and the other principal surface(reflecting surface) of the light guide plate 3. The present embodimentis the same as the foregoing first to fourth embodiments in this point;however, the characteristic feature of the present embodiment lies inthat the light guide plate 3 of the present embodiment particularlyincludes a polarization hologram layer 32 formed on a reflecting layer33 on the reflecting surface side of the light guide plate 3 as shown inFIG. 7.

The polarization hologram layer 32 of the present embodiment is providedfor changing the polarized state of light propagating in the light guideplate 3 to set the polarization direction of the light in theX-direction, i.e., the same direction as a transmission axis of apolarizing plate 65 of the liquid crystal display panel 6. With thisstructure, the polarizations of lights output from the light guide plate3 can be more aligned, thereby realizing a still higher transmissionefficiency of the liquid crystal display panel 6.

In the foregoing embodiment, the polarization hologram layer 32 isprovided on the reflecting surface side of the light guide plate 3.However, the present invention is not intended to be limited to theforegoing structure, and the polarization hologram layer may be formedon the light output surface side of the light guide plate 3 or both onthe reflecting surface and the light output surface.

Sixth Embodiment

Next, the sixth embodiment of the present invention is described. In thepresent embodiment, a plurality of deflectors having a fineconvexo-concave structure is formed on a reflecting surface in replaceof the scattering elements formed in the light guide plates of theforegoing first to fourth embodiments. Explanations on other structuresof the present invention which are in common with the foregoing first tofourth embodiments shall be omitted here. FIG. 8A is a perspective viewshowing a schematic structure of the light guide plate used in theplanar illumination device according to the present embodiment, FIG. 8Bis an enlarged plan view of a part B of FIG. 8A, and FIG. 8C is anenlarged section of a part A of FIG. 8A.

In a light guide plate 8 of the present embodiment, as shown in FIGS. 8Aand 8C, convexo-concave structures for diffracting, refracting orscattering incident lights in a thickness direction (Z-direction in FIG.8) of the light guide plate 8 are formed on light incident surfaces 8 aand 8 b, on which lights from light sources are incident. On the otherhand, a plurality of deflectors 9 having a fine convexo-concavestructure for changing propagation directions of lights incident on thelight guide plate 8 by an optical phenomenon such as reflection,scattering, refraction or diffraction are formed on the surface(reflecting surface) facing the output surface of the light guide plate8 as shown in FIG. 8B. Each deflector 9 is formed to have a reflectingsurface whose normal lies in the XZ plane or YZ plane and deflects lightincident on the light guide plate 8 to direct it toward the light outputsurface. The deflectors 9 may be formed by grooves formed in thereflecting surface of the light guide plate 8 by laser processing orgrooves integrally formed simultaneously with the molding of the lightguide plate 8.

In the planar illumination device according to the present embodiment,for example, lights emitted from the linear light source units 1 a and 1b of FIG. 1 are entered into the light guide plate 8, wherein theZ-polarized light is entered through the light incident surface 8 a andthe X-polarized light is entered through the light incident surface 8 b.The light entered through the light incident surface 8 a is scattered inthe Z-direction by the convexo-concave structure of the light incidentsurface 8 a and deflected by reflecting surfaces 9 a, whose normal liein XZ planes, of the deflectors 9 arranged on the reflecting surface tobe emitted from the light output surface as X-direction polarized light.

Similarly, the light entered through the light incident surface 8 b isscattered in the Z-direction by the convexo-concave structure of thelight incident surface 8 b and deflected by reflecting surfaces 9 b,whose normals lie in the YZ-planes, of the deflectors 9 arranged on thereflecting surface to be emitted from the light output surface as theX-direction polarized light.

The light outputted from the light guide plate 8 is incident on theliquid crystal display panel 6 after having an output angle distributioncorrected by a prism sheet, and most of this light passes through apolarizing plate 65 provided on the incident side so as to have atransmission axis in the X-direction.

According to the light guide plate of the present embodiment, thetransmission efficiency of the liquid crystal display panel can beimproved by aligning the polarizations of lights emitted from the planarillumination device and a liquid crystal display device with low powerconsumption can be realized.

Incidentally, the structure wherein the lights are incident on the lightguide plate from a plurality of directions is the same as those of theforegoing first to fourth embodiments, and an improved image quality canbe realized by making the luminance uniform.

Seventh Embodiment

Next, the seventh embodiment of the present invention is described. Inthe present embodiment, a reflecting plate is provided in replace of thelight guide plate of the foregoing sixth embodiment. Explanations onother structures of the present invention which are in common with theforegoing sixth embodiment shall be omitted here. FIG. 9 is aperspective view showing a schematic structure of a reflecting plateused in a planar illumination device according to the presentembodiment.

As shown in FIG. 9, a plurality of deflectors 91 having a fineconvexo-concave structure for changing propagation directions of lightsincident from light sources by an optical phenomenon such as reflection,scattering, refraction or diffraction are arranged on a reflectingsurface 81 of the present embodiment.

In the planar illumination device according to the present embodiment,for example, lights from the linear light source units 1 a and 1 b aredirected to the light guide plate 81, wherein the Z-polarized light isincident from the linear light source unit 1 a and the X-polarized lightis incident from the linear light source unit 1 b. The light incidentfrom the linear light source unit 1 a is deflected by reflectingsurfaces 91 a, whose normals lie in the XZ-planes, of the deflectors 91arranged on the reflecting surface 81 to be outputted to the liquidcrystal display panel 6 as the X-direction polarized light whilepropagating in the air on the side of the liquid crystal display panel 6of the reflecting plate.

Similarly, the light incident from the linear light source unit 1 b isdeflected by reflecting surfaces 91 b, whose normals lie in theYZ-planes, of the deflectors 91 arranged on the reflecting surface 81 tobe outputted to the liquid crystal display panel 6 as the lightpolarized in the X-direction light while propagating in the air on theside of the reflecting surface 81 toward the liquid crystal displaypanel 6.

By adopting the reflecting plate 81 of the present embodiment, thetransmission efficiency of the liquid crystal display panel can beimproved by aligning the polarizations of lights emitted from the planarillumination device and a liquid crystal display device with low powerconsumption can be realized similar to the foregoing sixth embodiment.Furthermore, higher image quality can be promoted by making theluminance uniform.

According to the planar illumination devices and the liquid crystaldisplay devices using the same according to the first to seventhembodiments of the present invention, it is possible to realize widecolor reproducibility and thin large screens by adopting laser lightsources, which provides high color purity, and which is suited for ahigh power output. It is also possible to realize large effects ofimproving image quality resulting from more uniform luminance, andreducing power consumption resulting from an improved utilizationefficiency of light.

Eighth Embodiment

Next, the eighth embodiment of the present invention is described. FIG.10A is a perspective view showing a schematic structure of a displayunit of a liquid crystal display device according to the eighthembodiment of the invention and FIG. 10B is an enlarged perspective viewof a part C of FIG. 10A.

As shown in FIG. 10A, the display unit of the liquid crystal displaydevice according to the present embodiment includes: a directillumination type backlight 101 in which LED devices of three primarycolors for emitting red, blue and green lights are arranged in a planarmanner, a diffusing plate 102 and a liquid crystal display panel 103. Asshown in FIG. 10B, the backlight 101 includes light source units 101 a,101 b and 101 c in each of which the LED devices are arranged.

According to the backlight 101 of the present embodiment, the LEDdevices of the light source unit 101 a are inclined so as to emit lightsto the left hand side, the LED devices of the light source unit 101 care inclined so as to emit lights to the right hand side, and the LEDdevices of the light source unit 101 b are arranged so as to emit lightsto be front side.

With reference to FIGS. 11A to 11C, a basic operation of the liquidcrystal display device according to the present embodiment is describedbelow. FIG. 11A is a front view showing the outer appearance of a liquidcrystal display device 104 according to the present embodiment. FIG. 11Bis a typical depiction showing a connection relationship of a humandetection sensor 105 of FIG. 11A, the light source units 101 a, 101 band 101 c of the backlight 101 and a controller 106 for controlling therespective light source units 101 a, 101 b and 101 c. FIG. 11C is ablock diagram showing a schematic structure of the controller 106 ofFIG. 11B.

As shown in FIG. 11A, the liquid crystal display device 104 according tothe present embodiment is provided with the human detection sensor 105for detecting the position of a user 123 watching videos displayed onthe liquid crystal display panel 103 of the display unit of the liquidcrystal display device 104. The human detection sensor 105 utilizes, forexample, electromagnetic waves for the position detection of the user123. Electromagnetic waves generated from the human detection sensor 105may be reflected from the user 123 and then the reflectedelectromagnetic waves may be detected by the human detection sensor 105.

As shown in FIG. 11B, the light source units 101 a, 101 b and 101 caccording to the present embodiment are controlled by the controller 106connected to the human detection sensor 105. The controller 106 includesa user position determining section 1061 and an illumination conditionsetting section 1062 as shown in FIG. 11C. The user position determiningsection 1061 obtains position indicative information of the user 123detected by the human detection sensor 105 and determines a positionalrelationship of the liquid crystal display device 104 and the user 123based on the position indicative information. The illumination conditionsetting section 1062 sets illumination conditions of the light sourceunits 101 a, 101 b and 101 c based on the determination result of theuser position determining section 1061. Here, the illumination conditionsetting sections 1062 sets respective amounts of lights to be emittedfrom the light source units 101 a, 101 b and 101 c for illuminationconditions, and the light in an amount as set for each of theillumination conditions is emitted from each of these light source units101 a, 101 b and 101 c.

In the liquid crystal display device 104 according to the presentembodiment, lights emitted from the respective light source units 101 a,101 b and 101 c of the backlight 1 have transmittances of the respectivecolors of red, blue and green controlled in the liquid crystal displaypanel 103 after being diffused by the diffusing plate 102, and an imageis color displayed on the front surface of the liquid crystal displaypanel 103.

Here, the luminance of an image displayed on the liquid crystal panel103 varies according to a viewing angle of the user 123 (hereinafterreferred to as “viewing angle characteristic”). Normally, the luminanceis highest when viewed from the front face, and the luminance becomeslower as the viewing angle is displaced from the front face. However,since the LED devices are inclined in the light source units 101 a and101 c of the present embodiment, the viewing angle characteristic ofonly lights emitted from the light source unit 101 a has a skewedluminance distribution to the left from the front of the screen, andlights emitted only from the light source unit 101 c have a viewingangle characteristic with a distribution opposite to that of the lightsemitted from the light source unit 101 a.

Next, an operation of controlling an amount of light by the controller106 is described. The user 123 shown in FIG. 11A is located more to theright side with respect to the front side of the screen of the liquidcrystal display device 104. Firstly, the human detection sensor 105detects the user 123 positioned more to the right with respect to thefront side of the screen of the liquid crystal display device 104 andtransmits this information to the controller 106. Based on thisinformation, the user position determining section 1061 determines thatthe user 123 is positioned more to the right with respect to the frontside of the screen of the liquid crystal display device 104 and sendsthe result of determination to the illumination condition settingsection 1062. The illumination condition setting section 1062 sets theemission amounts of the respective light source units 101 a, 101 b and101 c such that the amount of light emitted from the light source unit101 c is larger than those of the light source units 101 a and 101 b.Specifically, the illumination condition setting section 1062 sets therespective illumination conditions to increase the amount of lightemitted from the light source unit 101 c and to decrease the amounts oflights emitted from the light source units 101 a and 101 b. With theforegoing light amount control by the controller 106, the luminance at aline-of-sight angle from the right side of the screen increases toincrease visibility for the user 123 and luminance at other anglesdecrease to reduce power consumption.

According to the liquid crystal display device of the presentembodiment, the position of the user 123 is detected and the luminanceis controlled to increase in that direction, and the visibility isimproved and the power consumption is reduced by decreasing theluminance in other directions.

Generally, differences in viewing angle characteristics among therespective colors if any, cause a problem in that color changesaccording to viewing angles. In response, the present embodiment has adesirable structure wherein fine adjustments can be made on the amountsof lights in respective colors emitted at a plurality of output angles,thereby displaying a quality image with a wide viewing angle whilereducing variations in color.

In the present embodiment, the position of the user 123 is detected bythe human detection sensor 105. However, the present embodiment is notintended to be limited to this, and, for example, the user 123 may sethis position using a remote controller or the like.

In the present embodiment, the viewing angle characteristic of thebacklight 101 is controlled according to the direction toward the user123. However, the present embodiment is not intended to be limited tothis, and for example, the luminance of the backlight 101 may beadjusted as well according to distance between the user 123 and theliquid crystal display device 104. For example, when the user 123 ispositioned in a vicinity of the liquid crystal display device 104, areduction in power consumption can be realized by reducing the luminancein the direction toward the user 123.

In the case where a plurality of users are present around the liquidcrystal display device, power saving can be promoted by controlling theviewing angles in accordance with the positions of the users.Furthermore, by detecting the position of the user 123 in apredetermined cycle, a light amount control in conformity with themovement of the user 123 can be realized.

Ninth Embodiment

Next, the ninth embodiment of the present invention is described. Thecharacteristic structure of the present embodiment lies in the backlight101 of the foregoing eighth embodiment, which will be explained below.Explanations on other structures of the present invention which are incommon with the foregoing eighth embodiment shall be omitted here. FIGS.12A and 12B are enlarged perspective views of a light source unit of abacklight used in a liquid crystal display device according to thepresent embodiment.

As shown in FIG. 12A, the backlight of the present embodiment isarranged such that a light source unit 101 d made up of LED devicesarranged in a planar manner emits lights to the front face, and a lensarray 107 corresponding to the respective LED devices is provided. Theposition of the lens array 107 is controlled on a plane.

Specifically, the position of the lens array 107 is controlled by a lensarray driver 124 for moving the lens array 107. This lens array driver124 moves the lens array 107 in accordance with an illuminationcondition as set by an illumination condition setting section 1062.

Here, FIG. 12A shows a case where lights are emitted toward the frontside of the light source unit 101 d and FIG. 12B shows a case wherelights are emitted toward the right side of the light source unit 101 d.In FIG. 12B, emission directions of the lights are changed by displacingthe lens array 107 in a direction of “a” from the position of FIG. 12A.According to the foregoing structure, it is possible to make a fineadjustment of the emission direction, thereby realizing the effects asachieved from the foregoing eighth embodiment.

According to the foregoing structure, the viewing angle can be adjustedby moving the lens array 107 in an optical axis direction.

Furthermore, according to the present embodiment, both a light sourceunit with a fixed emission direction and a light source unit with avariable emission direction may be used as the light source units of thebacklight.

Tenth Embodiment

Next, the tenth embodiment of the present invention is described. Thepresent embodiment also has the characteristic structure in thebacklight 101 of the foregoing eighth embodiment. Explanations on otherstructures of the present invention which are in common with theforegoing eighth embodiment shall be omitted here. FIG. 13 is anenlarged side view of a light source unit of a backlight used in aliquid crystal display device according to the present embodiment.

As shown in FIG. 13, the backlight of the present embodiment is arrangedsuch that lights emitted from a light source unit 101 e are reflectedfrom mirrors 108, and emission directions are controlled by changing theangles of the mirrors 108 by rotating the mirrors 108 in directions “b”.The rotation of the mirrors 108 is controlled by a mirror driver 125 forrotating the mirrors 108, and the mirror driver 125 rotates the mirrors108 in accordance with an illumination condition set by an illuminationcondition setting section 1062.

In the present embodiment, both a light source unit with a fixedemission direction and a light source unit with a variable emissiondirection may be used as the light source units of the backlight.

Eleventh Embodiment

Next, the eleventh embodiment of the present invention is described. Inthe present embodiment, an edge light type backlight is adopted inreplace of the direct illumination type backlight of the foregoingeighth embodiment. Explanations on other structures of the presentinvention which are in common with the above eighth embodiment shall beomitted here. FIG. 14 is a perspective view showing a schematicstructure of a display unit of a liquid crystal display device accordingto the present embodiment.

A display unit of the liquid crystal display device according to thepresent embodiment is, as shown in FIG. 14, provided with an edge lighttype backlight 111, a prism sheet 115 and a liquid crystal display panel103. The backlight 111 includes light source units 112 a, 112 b and 112c made up of LED devices or laser light sources for emitting lights ofthree primary colors, i.e. red, green and blue lights, and a light guideplate 113. As in the structure of the first embodiment, a multitude ofisotropic scattering elements 114 having no directivity are uniformlyarranged in the light guide plate 113, and incident lights from thelight source units 112 a, 112 b and 112 c are equally deflected in everydirection by an optical phenomenon such as reflection, scattering,refraction or diffraction caused by the multitude of scattering elements114. The prism sheet 115 is the one for deflecting output angles in theY-direction of FIG. 14.

Although not shown, the backlight 111 of the present embodiment isinstalled in a liquid crystal display device similar to that of theabove eighth embodiment and is arranged such that amounts of lightemitted from the light source units 112 a, 112 b and 112 c can becontrolled based on the information from a human detection sensor.Specifically, the backlight 111 of the present embodiment includes anemission amount adjuster 126 for adjusting the amounts of lightsrespectively emitted from the light source units 112 a, 112 b and 112 c,and the emission amount adjuster 126 adjusts the amounts of lightsemitted in accordance with the illumination conditions set by theillumination condition setting section 1062.

In the liquid crystal display device according to the presentembodiment, lights emitted from the light source units 112 a, 112 b and112 c are incident on the light guide plate 113 and deflected by thescattering elements 114 in the light guide plate 113 to be emitted fromthe light guide plate 113. Here, since the majority of the lightsincident on the light guide plate 113 are emitted while being biased ina direction opposite to incident directions, the viewing anglecharacteristic of light emitted from the light source unit 112 a has amaximum luminance in a negative direction along an X axis of FIG. 14 andlight emitted from the light source unit 112 c is opposite to the lightemitted from the light source unit 112 a. Furthermore, the light emittedfrom the light source unit 112 b has a viewing angle characteristicbiased in the Y direction of FIG. 14; however, comes to have a viewingangle characteristic with a maximum luminance to the front side of thebacklight by having an output angle thereof deflected by the prism sheet115.

The lights emitted from the light source units 112 a and 112 c andpassed through the prism sheet 115 and the light from the light sourceunit 112 b deflected by the prism sheet 115 have the transmittances ofthe respective colors of red, blue and green controlled in the liquidcrystal display panel 103, thereby displaying a color image on the frontsurface of the liquid crystal display panel 103.

Here, in the case where a user is positioned, for example, more to theright (positive direction of an X axis of FIG. 14) with respect to thefront side of the screen of the liquid crystal display panel, the humandetection sensor 105 detects the user 123 located more to the right withrespect to the front side of the screen of the liquid crystal displaydevice 104 and this information is sent to the controller 106.Subsequently, based on this information, a user position determiningsection 1061 determines that the user 123 is located more to the rightthan the front side of the screen of the liquid crystal display device104 and sends the result of determination to the illumination conditionsetting section 1062. The illumination condition setting section 1062sets the respective emission quantities of the light source units 112 a,112 b and 112 c such that the amount of lights emitted from the lightsource unit 112 c is larger than those of the light source units 112 aand 112 b. Specifically, the illumination condition setting section 1062sets the respective illumination conditions to increase the amount oflight emitted from the light source unit 112 c and to decrease theamounts of lights emitted from the light source units 112 a and 112 b.The emission amount adjuster 126 adjusts the respective amounts oflights emitted from the light source units 112 a and 112 b in accordancewith the illumination conditions set by the illumination conditionsetting section 1062. With the foregoing emission amount control of theemission amount adjuster 126, the luminance at a line-of-sight anglefrom the right side of the screen increases to increase visibility forthe user 123 and luminances at other angles decrease, therebysuppressing power consumption.

Also in the liquid crystal display device of the present embodiment, theposition of the user is detected and the luminance is controlled toincrease in that direction, and visibility is improved and powerconsumption is reduced by decreasing luminance in other directions.

When using a laser light source as a light source, the effect ofincreasing the luminance in a necessary direction and decreasing it inan unwanted direction is further improved since the directivity ishigher as compared with the case of LED devices. In this case, if thedirectivity of laser lights in the light guide plate 113 is too high,the range of an output angle of light emitted from the light guide plate113 can be widened to obtain the output light with a suitable degree ofscattering by providing a convexo-concave structure for diffracting,refracting or scattering light in a thickness direction on the lightincident surface of the light guide plate 113.

Twelfth Embodiment

Next, the twelfth embodiment of the present invention is described. Inthe present embodiment, a plurality of deflectors having a fineconvexo-concave structure are arranged on the reflecting surface inreplace of the scattering elements provided in the light guide plate ofthe foregoing eleventh embodiment. Explanations on other structures ofthe present invention which are in common with the foregoing eleventhembodiment shall be omitted here. FIG. 15A is a perspective view showingthe schematic structure of a light guide plate used in a liquid crystaldisplay device according to the present embodiment and FIG. 15B is anenlarged plan view of a part D of FIG. 15A.

As shown in FIGS. 15A and 15B, a plurality of deflectors 117 having sucha fine convexo-concave structure for deflecting and emitting lightsincident through different end surfaces in different directions arearranged on a surface (reflecting surface) facing a light output surfacein a light guide plate 116 of the present embodiment.

In the liquid crystal display device according to the presentembodiment, light source units 112 a, 112 b and 112 c are semiconductorlaser devices and lights with high directivity are incident while beingsuitably diffused by the convexo-concave structures of the respectivelight incident surfaces of the light guide plate 116. Each deflector 117on the reflecting surface of the light guide plate 116 is formed to havea reflecting surface whose normal lies in an XZ plane or YZ plane, andlights incident from the light source units 112 a, 112 b and 112 c areemitted in different directions in the XZ plane. Thus, effects similarto those of the above eleventh embodiment are obtained.

Thirteenth Embodiment

Next, the thirteenth embodiment of the present invention is described.In the foregoing eleventh and twelfth embodiments, the light sourceunits are provided in the outside of the light guide plate. In contrast,in the present embodiment, light source units are provided on theunderside of a light guide plate and lights are incident on the lightguide plate while being deflected by mirrors or the like. FIG. 16A is aside view showing a schematic structure of a backlight 111 according tothe present embodiment and FIG. 16B is a rear view of the backlightincluding a part E of FIG. 16A.

The backlight 111 of the present embodiment is, as shown in FIGS. 16Aand 16 b, provided with a light guide plate 113, two light source units119 a and 119 b arranged on the underside of the light guide plate 113for combining and emitting lights with aligned polarizations from laserlight sources of three primary colors, prisms 118 a, 118 b and 118 c forintroducing lights from the light source units 119 a and 119 b on theunderside of the light guide plate 113 to end surfaces of the lightguide plate 113, half wave plates 120 a and 120 b for rotating thepolarizations of the lights from the light source units 119 a and 119 b,polarization beam splitters 121 a and 121 b, and linearization opticalelements 122 a, 122 b and 122 c which are lenticular lenses, cylindricallenses or the like. The orientations of the optical axes of the halfwave plates 120 a and 120 b are controlled by a half wave plate opticalaxis adjuster 127, so that the polarizations of the lights from thelight source units 119 a and 119 b can be controlled. The half waveplate optical axis adjuster 127 changes the orientations of the opticalaxes of the half wave plates 120 a and 120 b in accordance withillumination conditions set by an illumination condition setting section1062.

Since the polarizations of lights emitted from the light source units119 a and 119 b can be freely changed by the two wave plates 120 a and120 b in the backlight 111 of the present embodiment, ratios of lightspassing through and reflected from the polarization beam splitters 121 aand 121 b can be controlled.

According to the foregoing structure, lights incident on the light guideplate 113 via the linearization optical elements 122 a, 122 b and 122 cand the prisms 118, 118 b and 118 c have different output anglesdepending on the end surfaces on which they are incident, and amounts oflight thereof can be controlled individually. As a result, the effectsas achieved from the foregoing eleventh and twelfth embodiments can beachieved.

According to the liquid crystal display devices of the eighth to thethirteenth embodiments of the present invention, it is possible toobtain a large effect of reducing power consumption by reducing theluminance in unnecessary directions in which the user is not presentwhile ensuring sufficient luminance in a necessary direction bydetecting the position of the user.

Furthermore, by suppressing changes in color when the screen is viewedin an oblique direction, a liquid crystal display device with a highviewing angle and high image quality can be realized.

The present invention is summarized as follows from the above respectiveembodiments. Specifically, a planar illumination device according to oneaspect of the present invention for illuminating a liquid crystaldisplay panel provided with a polarizing plate on a light incident side,includes: a light source unit for emitting light having a specifiedpolarization direction; and a light irradiating member for deflectinglight emitted from the light source unit and irradiating the liquidcrystal display panel with the deflected light, wherein the lightirradiating member deflects the light emitted from the light source unitsuch that the polarization direction of the light emitted from the lightsource unit substantially coincides with a transmission axis directionof the polarizing plate of the liquid crystal display panel.

According to the foregoing structure of the planar illumination device,the liquid crystal display panel is irradiated with the light emittedfrom the light source unit in such a manner that the polarizationdirection thereof is brought into substantially coincide with thetransmission axis direction of the liquid crystal display panel. Withthis structure, the transmission efficiency of the liquid crystaldisplay panel can be improved, thereby realizing improved lightutilization efficiency while reducing power consumption.

It is preferable that the light source unit includes either a firstlight source for emitting light having a polarization directionsubstantially orthogonal to a surface of the polarizing plate to beincident on the light irradiating member in the transmission axisdirection of the polarizing plate or a second light source for emittinglight having a polarization direction substantially parallel to thesurface of the polarizing plate to be incident on the light irradiatingmember in a direction orthogonal to the transmission axis direction ofthe polarizing plate. It is also preferable that the light sourceincludes the first light source and the second light source; and lightsfrom the first and second light sources are incident on the lightirradiating member in directions orthogonal to each other.

According to the foregoing structure, the polarization directions of therespective lights emitted from the first and second light sources can bebrought into substantially coincide with the transmission axis directionof the polarizing plate of the liquid crystal display panel.

With the foregoing structure, it is preferable that the lightirradiating member be a light guide plate having a first end surfacesubstantially vertical to a transmission axis of the polarizing plate, asecond end surface orthogonal to the first end surface, a firstprincipal surface from which incident lights through the first andsecond end surfaces are emitted, and a second principal surface facingthe first principal surface.

According to the foregoing structure, the lights emitted from the firstand second light sources can be incident through the two orthogonal endsurfaces and the liquid crystal display panel can be irradiated with therespective emitted lights having the polarization directions thereofbrought into substantially coincide with the transmission axis directionof the liquid crystal display panel. It is therefore possible to realizea uniform luminance of a liquid crystal display panel with a large areaand to display an image of an improved quality.

The light guide plate preferably includes therein a plurality ofisotropic scattering elements for deflecting the respective lightsemitted from the first and second light sources.

According to the foregoing structure, the respective lights emitted fromthe first and second light sources can be equally scattered in everydirection within the light guide plate. It is therefore possible todirect the respective lights emitted from the first and second lightsources respectively to the first principal surface at substantially thesame efficiency.

It is preferable that the plurality of scattering elements be formedwithin the light guide plate at uniform intensities.

According to the foregoing structure, the scattering elements aredistributed within the light guide plate at uniform density. It istherefore possible to direct the respective lights emitted from thefirst and second light sources respectively to the first principalsurface at the same efficiency.

It is preferable that a plurality of fine members for deflecting therespective lights emitted from the first and second light sources indirections toward the first principal surface are formed on the secondprincipal surface of the light guide plate; each of the plurality offine members has a first reflecting surface having a normal in a virtualplane vertical to the first principal surface and orthogonal to thefirst end surface and a second reflecting surface having a normal in avirtual plane vertical to the first principal surface and orthogonal tothe second end surface; and the first and second reflecting surfacesreflect the lights respectively emitted from the first and second lightsources toward the first principal surface.

According to the foregoing structure, since the respective lightsemitted from the first and second light sources are reflected from thefirst and second reflecting surfaces toward the first principal surface.It is therefore possible to make the efficiency of directing the lightemitted from the first light source to the first principle surface moreequal to the efficiency of directing the light emitted from the secondlight source to the first principle surface.

It is preferable that the plurality of fine members have the same shapeand are periodically formed on the second principal surface.

According to the foregoing structure, the plurality of fine members inthe same shape are periodically distributed on the second principalsurface. It is therefore possible to make it closer to one another therespective efficiencies of directing the light emitted from the firstlight source to the first principle surface and directing the lightemitted from the second light source to the first principle surface.

It is preferable that the light guide plate further include apolarization hologram layer arranged on the second principal surface andadapted to align the polarization directions of the respective lightsemitted from the first and second light sources so that the polarizationdirections of the respective lights emitted from the first and secondlight sources substantially coincide with the transmission axisdirection of the liquid crystal display panel.

According to the foregoing structure, the polarization directions of therespective lights emitted from the first and second light sources can bealigned. It is therefore possible to make the polarization directions ofthe respective lights emitted from the first and second light sources bemore approximated to the transmission axis direction of the liquidcrystal display panel.

The light irradiating member is preferably the light irradiating memberis a reflecting plate having a flat surface provided on a side of theliquid crystal display panel, a first side substantially vertical to thetransmission axis direction of the polarizing plate and a second sideorthogonal to the first side and adapted to reflect the respectivelights emitted from the first and second light sources on the flatsurface to be outputted to the side of the liquid crystal display panel.

According to the foregoing structure, it is possible to simplify thestructure of the light irradiating member.

It is preferable that a plurality of fine members for deflecting therespective lights emitted from the first and second light sources indirections to the side of the liquid crystal display panel are formed onthe flat surface; each of the plurality of fine members has a firstreflecting surface having a normal in a virtual plane vertical to theflat surface and orthogonal to the first side and a second reflectingsurface having a normal in a virtual plane vertical to the flat surfaceand orthogonal to the second side; and the first and second reflectingsurfaces reflect the lights emitted from the first and second lightsources toward the liquid crystal display panel.

According to the foregoing structure, the respective lights emitted fromthe first and second light sources can be reflected from the first andsecond reflecting surfaces toward the first principal surface. It istherefore possible to make the polarization directions of the respectivelights emitted from the first and second light sources be moreapproximated to the transmission axis direction of the liquid crystaldisplay panel.

It is preferable that the plurality of fine members have the same shapeand periodically formed on the second principal surface.

According to the foregoing structure, the plurality of fine members inthe same shape are periodically distributed on the plane on the side ofthe liquid crystal display panel. It is therefore possible to make itcloser to one another the respective efficiencies of directing the lightemitted from the first light source to the first principle surface anddirecting the light emitted from the second light source to the firstprinciple surface.

It is preferable to further include: a half wave plate for rotating thepolarization direction of light emitted from the light source unit; anda polarization beam splitter for splitting the light having passedthrough the half wave plate into first and second polarizationcomponents, transmitting light of the first polarization component andreflecting light of the second polarization component, wherein thepolarization beam splitter is provided so as to face the secondprincipal surface of the light guide plate and emits either one of thelights of the first and second polarization components as a lightemitted from the first light source while emitting the other as a lightemitted from the second light source.

According to the foregoing structure, a light emitted from one lightsource unit can be split into a light emitted from the first lightsource and a light emitted from the second light source. It is thereforepossible to reduce the number of the light source units. Furthermore,the polarization beam splitter for splitting the light emitted from onelight source unit is provided so as to face the second principal surfaceof the light guide plate. It is therefore possible to prevent anincrease in size of the device.

It is preferable to further include a lightguide for guiding lightemitted from the light source unit; and a polarization beam splitter forsplitting the light guided by the light guide into first and secondpolarization components, transmitting light of the first polarizationcomponent and reflecting light of the second polarization component;wherein the polarization beam splitter is provided so as to face thesecond principal surface of the light guide plate and emits either oneof the lights of the first and second polarization components as a lightemitted from the first light source while emitting the other as a lightemitted from the second light source.

According to the foregoing structure, lights emitted from one lightsource unit can be split and emitted as the light emitted from the firstlight source and the light emitted from the second light source. It istherefore possible to emit two lights without increasing the number ofthe light source unit. Furthermore, the polarization beam splitter forsplitting the light emitted from one light source unit is provided so asto face the second principal surface of the light guide plate. It istherefore possible to prevent an increase in size of the device.

It is preferable that either one of the first and second light sourcesemit a green light; and the other one of the first and second lightsources emits red and blue lights.

According to the foregoing structure, even if the size of the lightsource for emitting green light is larger than that of the light sourcefor emitting red and blue lights, a degree of freedom in arranging thelight sources can be increased since an end surface on which the greenlight is incident is provided independently of an end surface on whichthe red and blue lights are incident.

It is preferable that either one of the first and second light sourcesemit a blue light; and the blue light is emitted in a directionsubstantially parallel to the shorter one of two sides of the firstprincipal surface orthogonal to each other.

According to the foregoing structure, a traveling distance of the bluelight in the light guide plate can be made shorter. It is thereforepossible to reduce the attenuation of blue light power in the lightguide plate.

The light source unit is preferably a laser light source unit.

According to the foregoing structure, the polarized nature of the lightemitted from the light source unit can be intensified. It is thereforepossible to more approximate the polarization direction of light emittedfrom the light source unit to the transmission axis direction of theliquid crystal display panel.

The light source unit preferably includes LED devices and a polarizingelement for polarizing lights emitted from the LED devices in apredetermined direction.

According to the foregoing structure, the light having a specifiedpolarization direction can be emitted using inexpensive LED devices. Itis therefore possible to reduce the cost of the light source unit.

It is preferable to further include a controller for controlling thehalf wave plate, wherein the controller changes a ratio of the lights ofthe first and second polarization components split by the polarizationbeam splitter by rotating the polarization direction of the lightemitted from the light source unit using the half wave plate.

According to the foregoing structure, the polarization directions of thelights emitted from the light source unit can be freely changed. It istherefore possible to control the ratio of the lights of the first andsecond polarization components split by the polarization beam splitter.

A liquid crystal display device according to another aspect of thepresent invention comprises the above planar illumination device and aliquid crystal display panel to be illuminated by the planarillumination device, wherein a polarization direction of lightirradiated from the planar illumination device substantially coincideswith a transmission axis of the polarizing plate.

According to the foregoing structure of the liquid crystal displaydevice, the transmission efficiency of the liquid crystal display panelcan be increased by irradiating the liquid crystal display panel withthe light emitted from the light source unit and having the polarizationdirection thereof brought into substantially coincide with thetransmission axis direction of the liquid crystal display panel. It istherefore possible to realize a liquid crystal display device with highlight utilization efficiency and low power consumption.

It is preferable to further include a sensor for detecting the positionof a user viewing an image displayed on the liquid crystal display paneland an adjuster for adjusting an amount of light emitted from the lightsource unit based on the detection result by the sensor.

With the foregoing structure, the amount of light emitted from the lightsource unit can be so adjusted as to improve visibility for the user inaccordance with the position of the user.

INDUSTRIAL APPLICABILITY

A planar illumination device and a liquid crystal display device usingthe same according to the present invention can realize, a thin largescreen with wide color reproducibility and can realize a liquid crystaldisplay device with high image quality and low power consumption byuniformizing the luminance of the planar illumination device andimproving light utilization efficiency, wherefore they are useful in thedisplay field.

1. A planar illumination device that illuminates a liquid crystaldisplay panel, comprising: a light source unit that emits light towardthe liquid crystal display panel; an optical element that is disposed onan optical path of the light emitted from the light source unit; and adriver that drives the optical element, wherein the driver drives theoptical element to control a direction of the light that illuminates theliquid crystal display panel.
 2. The planar illumination deviceaccording to claim 1, wherein the optical element includes a lens, andthe driver moves a position of the lens to control the direction of thelight that illuminates the liquid crystal display panel.
 3. The planarillumination device according to claim 2, wherein the optical elementincludes a lens array as the lens.
 4. The planar illumination deviceaccording to claim 1, wherein the optical element includes a mirror, andthe driver rotates the mirror to change an incident angle of lightincident on the mirror to control the direction of the light thatilluminates the liquid crystal display panel.
 5. The planar illuminationdevice according to claim 1, further comprising a human detection sensorthat detects a position of a user, wherein the driver drives the opticalelement based on a detection result of the human detection sensor tocontrol the direction of the light that illuminates the liquid crystaldisplay panel.
 6. The planar illumination device according to claim 1,wherein the light source unit includes a plurality of LED devices whichare arranged side by side.
 7. A liquid crystal display device,comprising: the planar illumination device according to claim 1; and aliquid crystal display panel that is illuminated by the planarillumination device.